Metallic wood-boring beetles

Agrilus spp.

1. Identification

• Common name: Metallic wood-boring beetles
• Scientific name: Agrilus spp. (several species, including relevant pests such as A. planipennis Fairmaire, A. biguttatus Fabricius and A. sulcicollis Lacordaire)
• Order: Coleoptera
• Family: Buprestidae

2. Pest description

• Adults: Elongated beetles, 6–15 mm, with metallic green, bluish or bronze colouration; flattened and shiny body; activity mainly on hot and sunny days.
• Larvae: Apodous, flattened and serpentiform, cream-coloured; bore sinuous galleries in the cambium and surface wood, interrupting the flow of sap.
• Pupae: Formed inside the wood, in oval pupal chambers.
• Eggs: Laid in cracks of the bark or on the surface of the trunk.

3. Main hosts

• Various broadleaved trees, notably oaks, ashes, birches and poplars.
• Some species attack ornamental and urban trees, especially when weakened by drought, soil compaction or other stress factors.
• In Mediterranean forests, species such as A. biguttatus are associated with oak decline.

4. Symptoms and damage

• “D”-shaped emergence holes, characteristic of buprestids.
• Sinuous galleries under the bark, interrupting the flow of sap and causing cambial necrosis.
• Drying of upper branches, with downward progression.
• Yellowing, partial defoliation and loss of vigour.
• Longitudinal cracks in the bark due to larval activity.
• In severe attacks, they can cause rapid decline and death of the tree, especially in sensitive species such as ashes and oaks.

5. Biological cycle

• One annual generation in most species, possibly extending over two years in colder climates.
• Adults emerge in spring and summer, feeding on leaves before egg-laying.
• Larvae develop under the bark for several months, boring extensive galleries.
• Pupation inside the wood, with the emergence of adults the following year.
• Development favoured by high temperatures, prolonged droughts and weakened trees.

6. Monitoring

• Observation of “D”-shaped emergence holes.
• Inspection of upper branches and trunks to detect drying and necrosis.
• Assessment of galleries under the bark in suspect trees.
• Reinforced monitoring in areas with decline of oaks or ashes.
• Chromotropic traps and pheromones may be used for the detection of some species.

7. Management measures

• Cultural: Removal and destruction of heavily affected trees; improvement of stand vitality; avoiding injuries to the trunk.
• Preventive: Reduction of water stress; adequate density management; avoiding the accumulation of dead wood that may attract adults.
• Integrated protection: Regular monitoring; intervention only when necessary; practices that reduce the attractiveness of weakened trees; attention to the legal framework, given that invasive species such as Agrilus planipennis are regulated as quarantine pests in the European Union under Regulation (EU) 2016/2031 on plant health protection.

Bibliographic references

• EPPO Global Database – Agrilus spp.
• CABI Invasive Species Compendium – Agrilus spp.
• Haack, R. A. et al. (2002). Buprestid beetles and their impact on forest health.
• Regulation (EU) 2016/2031 – Protection against quarantine pests in the European Union.